ΔE 10.1, fair: the same colour family, but not a straight swap. IJN Gray (Kure Arsenal) is a little darker than Tanker Grey.
Can I use IJN Gray (Kure Arsenal) instead of Tanker Grey?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). IJN Gray (Kure Arsenal) is a little darker than Tanker Grey.
Can I use Tanker Grey instead of IJN Gray (Kure Arsenal)?
The same difference applies the other way round: Tanker Grey is a little lighter.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.